Ionic Mobility of Cation and Anion of Lithium Gel Electrolytes Measured by Pulsed Gradient Spin−Echo NMR Technique under Direct Electric Field

Abstract

The ionic mobilities of the individual cations and anions of the lithium gel electrolyte, LiN(CF3SO2)2−EC/DEC−PVdF-HFP, were measured using the pulsed gradient spin−echo (PGSE) NMR by applying a direct electric field during the spin−echo measurements. Theoretical expressions of the echo intensity were derived by considering the effect of chemical exchange between the ion and the ion pair in the electrolyte in order to clarify the physical meaning of the experimental results. Under the potential application below 30 V, the conductivities of the lithium ion and the anion were estimated to be 3.6 × 10-5 and 9.4 × 10-5 cm2 s-1 V-1, respectively. This is the first result describing the mobilities of both the cations and anions in the electrolyte that was directly measured by the combination of NMR spectroscopy and an electrochemical technique for the extraction of the individual ionic properties of migration.